Warp-knitted fabric



Oct. 1 1968 B. J. GAJJAR 3, I

WARP-KNITTED FABRIC Filed Nov. 19, 1965 INVENTOR BHARAT JAYBHADRA GAJJAR ATTORNEY- United States Patent 3,403,537 WARP-KNITTED FABRIC Bharat Jaybhadra Gajjar, Wilmington, Del., assignor to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware Filed Nov. 19, 1965, Ser. No. 508,787 1 Claim. (Cl. 66195) ABSTRACT OF THE DISCLOSURE A two-bar warp-knitted fabric composed of randomly textured and conventional untextured yarns. The relative tensions on the yarns during knitting of the fabric are adjusted so that loops of the textured yarn are larger than those of the conventional yarn.

This invention relates to a warp-knitted, crepe-like fabric and, more particularly, to a two-bar warp-knitted fabric composed of jet pretextured and nontextured synthetic fibers.

Generally, creping of fabric results from longitudinal contraction of yarn to which a high level of twist has been imparted, which yarn exhibits a great tendency to untwist when freed from restraint and thus may be said to possess a large amount of latent torsional energy. This tendency to luntwist is a characteristic common to all yarns regardless of their chemical nature of composition. Prior art processes for preparing the yarn for crepe fabrics, however, involve expensive techniques as, for example, introduction of excessive high twist into the yarn, usually by two-step process or by steaming during twisting; preparation of a composite yarn by plying together shrinkable and nonshrinkable yarns; treatment of the yarn with a chemical softening or swelling agent, which results in a fabric of relatively little strength; or by other means which yield a fiat-faced fabric having little or none of the appearance of a true crepe.

It is an object of this invention to produce crepe-like tricot structures by employing a jet pretextured synthetic fiber on one bar of a two-bar warp-knitting machine.

This and other objects will become apparent in the course of the following specification and claims.

In accordance with the invention, a two-bar Warpknitted fabric composed of textured and untextured yarn is provided. By a jet pretextured yarn is meant a high denier-per-filament (-25 d.p.f.) yarn having 1, 2 or 3 filaments per yarn bundle which has been textured by passing it through a bulking jet, as disclosed in Breen and Lauterback U.S. Patent 3,186,155. In this process, a stream of compressible fluid at a temperature above the second-order transition temperature of the polymer of which the filament is made and preferably at least about 300 F. is vigorously jetted to form a turbulent plasticizing region. The yarn or filaments to be treated are positively fed at a rate greater than the yarn takeup speed into the fluid plasticizing stream so that the yarn is supported by it and individual filaments are separated from each other and crimped individually by whipping about in the hot turbulent plasticizing region, and rapidly cooled while being maintained at low tension to set the convolutions. Under these conditions the yarn temperature is above the cold point (I. App. Physics, 20, 499 (1949)) and below the melting point of the yarn. During the jetting treatment, filament shrinkage occurs because of the heat transmitted to the fibers. The process elements such as temperature, pressure, fiuid flow, yarn speed, tension, and windup speed are adjusted so as to give a final yarn denier (measured in relaxed form after hot-wet relaxation) greater than the feed yarn denier and preferably at least 30% greater than the feed yarn denier.

The individual filaments of the pretextured yarn are characterized by possessing alternate S and Z twist sections throughout their lengths, with at least one S turn and at least one Z turn per inch of filament which have a twist angle averaging at least 5. This twist is further characterized by random variation along the filament length, having a random number of turns between twist reversals, having a random continuously varying angle of twist along its length, and having a random number of twist reversals per inch. Nevertheless, the filaments are free from cross-sectional deformation, as contrasted to the deformed cross-sections characteristic of gear-crimped filaments and those produced by mechanical bulking processes in general. The fabric is knitted by feeding one of the two yarns at the top front bar of a knitting machine and by feeding another yarn at the bottom back bar of the machine. A conventional spun or continuous yarn is fed to one bar, while a jet pretextured yarn is fed to either the top front or bottom back bar. Because the jet pretextured yarn crimps further when the fabric is scoured, the feed of the two yarns is controlled to provide a ratio of loop length of jet pretextured yarn to conventional yarn of from about 1.111 to about 1.4:1. The fabric, after finishing, has a crepe-like appearance since on exposure to hot water, further increase in crimp amplitude and frequency of the pretextured yarn is obtained. Preferably the jet pretextured feed yarn is a continuous filament nylon. However, polyamides, copolyamides, polyesters, copolyesters, polyacrylonitrile, polypropylene, regenerated cellulose and cellulose acetate are suitable as yarn materials. The nature of the conventional yarn is not important.

The novel crepe-like fabrics of the invention will be further understood by reference to the drawings wherein:

FIGURE 1 is a loop diagram of the front of a greige tricot fabric (jersey stitch) of this invention showing the jet pretextured and conventional yarn.

FIGURE 2 illustrates the appearance of the yarns of FIGURE 1 in the finished fabric.

In the fabric stitch shown in the figures, yarn 10 forming the larger loop is the jet pretextured randomly crimped filament. The loop length of yarn 10 is the distance from point a around the loop, and back to that point. Similarly, the loop length of conventional yarn 12 (the smaller loop) is the distance from point b, around the loop, and back to that point. The loop length of the yarns may be determined using a microscope and measuring the indicated distances.

The novel Warp-knitted fabrics of the invention are conveniently knitted on an ordinary knitting machine. The jet pretextured yarn may be fed to either the top front bar or to the bottom back bar of the machine. The relative tensions upon the yarns fed to the machine are adjusted so that the loops of the jet pretextured yarn are larger than those of the conventional yarn. The larger loops are formed so as to have a loop length which is from 1.1 to 1.4 times the loop length of the conventional yarn. Ordinarily, this can be achieved in a jersey fabric if the fabric is knitted in such a manner that the random loop crimped component front bar to regular component back bar actual knitting ratio is at least about 1.40.

While light denier, low denier-per-filament jet pretextured yarns do not provide acceptable knitting performance, the light denier, high denier-per-filament jet pretextured yarns display excellent knitting performance. The knitting performance of the textured yarn is measured in racks per end out where a rack is 480 courses and an end out is a defect caused by a missing or broken end.

Quality hereinafter referred to is a quantitative measure of the number of inches of fabric per rack as, for example,

a fabric knitted with 6" quality is knitted with 480 courses or one rack in each 6 of fabric.

The invention provides a fabric having a crepe-like appearance and good cover due to the further crimping of the jet pretextured yarn when the fabric is finished by procedures normally used such as scouring, heating, bleaching and drying. The pretextured randomly crimped yarn, during shrinkage, distorts the loops of conventional yarn so that a random out of phase rather than an in line relationship exists between stitches as shown in FIG- URE 2.

The covering power of the warp knit fabrics described in the specification is measured in terms of the percent of normal incident white light passing through the fabric and is designated as percent I The following example is given to illustrate the invention and is not intended to be limiting.

Example I Four jersey fabrics designated A, B, C, and D are knitted on a two-bar, 28-gauge tricot machine. The stitch pattern used is 2-3, 1-0 front bar and 1-0, 1-2 back bar. The yarn layout of fabrics A and B are 20 denier, 7 filament, 1/2 turn Z twist nylon conventional filament yarn on the front bar and 15 denier jet pretextured nylon monofilament on the back bar. Fabric A is knitted with 8" quality, front runner 56", back runner 40" for a 1.4 ratio. Fabric B is knitted with 6 quality, front runner 51", back runner 39.5 for a 1.3 ratio.

The yarn layout of fabric C is 37 denier, 13 filament jet pretextured nylon filament yarn on the front bar and 30 denier, filament, 1/2 turn Z twist nylon conventional filament yarn on the back bar with 7" quality, front runner 60", back runner 42" for a 1.4 ratio.

The yarn layout of fabric D is 15 denier Zero twist nylon conventional monofilament on the front bar and denier, 7 filament, 1/2 turn Z twist nylon conventional filament yarn on the back bar with 7" quality, front runner 52.5", back runner 37.5" for a 1.4 ratio.

The knitting performance and physical properties of the greige fabrics are as follows:

Each of the four fabrics is scoured at boil for /2 hour, then tumble dried, then heat-set, bleached and dried. Fabrics A, B, and C have a crepe-like appearance. Fabric D, containing no jet pretextured yarn, has a conventional tricot-knit apearance. The physical properties of the finished fabrics are shown in Table 2.

TABLE 2 Piece Weight, Wales Courses Thickness Bulk, Percent No. oz. Iyd. per per inch, cc. lg It inch inch 5 g./cm.

A--. 2.2 68.0 65.0 0.0171 5.82 7.0 B 2.3 72.0 65.0 0.0155 5.23 8.3 C 2. 4 57.0 55.0 0. 0178 5. 58 3.18 D 1. 5 59. 0 60.0 0. 0092 4. 01 28.0

It is significant that while the fabrics incorporating jet pretextured yarns (A, B, C) exhibit greater covering power as compared to warp knitted fabrics of the prior art (D), only fabrics A and B of the group using jet pretextured yarn of appropriate denier have an acceptable knitting performance.

The improved covering power results from a different structure of the final fabric wherein the shrinkage of the jet pretextured yarn distorts the nontextured yarn in a random phase relationship thus allowing more efficient use of the yarns in blocking the passage of light through the fabric. The invention also permits the use of lighter weight tricot fabrics having covering power equal to that of heavier conventional fabrics. The tricot fabrics of this invention may be used to produce slips, gowns, lingerie and other undergarment fabrics, as well as dresses, blouses and other outerwear garments.

It will be apparent that many different embodiments may be made without departing from the spirit and scope of this invention; therefore it is not intended to be limtied except by the scope of the appended claim.

What is claimed is:

1. A two-bar, warp-knitted fabric wherein the stitches are formed of first and second synthetic filamentary yarns, the ratio of the loop length of said first yarn to the loop length of the second yarn being between about 1.1 to 1.4:], said first yarn being jet pretextured and having individual filaments characterized by possessing alternate S and Z twist sections throughout their lengths, with at least one S turn and at least one Z turn per inch of filament which have a twist angle averaging at least 5, the said twist being further characterized by random variation along the filament length, a random number of turns between twist reversals, a random continuously varying angle of twist along its length, and a random number of twist versals per inch, said second synthetic filamentary yarn being of a conventional construction and being distorted by the pretextured yarn in a random phase relationship.

References Cited UNITED STATES PATENTS 3,041,861 7/1962 Kasey 66-195 3,069,885 12/1962 Cooper et a1 66-l95 3,186,155 6/1965 Brcen et a1 57-157 X 3,254,510 6/1966 Lesley 66-195 MERVIN STEIN, Primary Examiner. 

